R: t test over multiple columns using t.test function

Question

I tried to perform independent t-test for many columns of a dataframe. For example, i created a data frame

set seed(333)
a <- rnorm(20, 10, 1)
b <- rno         


        

Answer 1

Simply extract the estimate and p-value results from t.test call while iterating through all needed columns with sapply. Build formulas from a character vector and transpose with t() for output:

formulas <- paste(names(test_data)[1:(ncol(test_data)-1)], "~ grp")

output <- t(sapply(formulas, function(f) {      
  res <- t.test(as.formula(f))
  c(res$estimate, p.value=res$p.value)      
}))

Input data (seeded for reproducibility)

set.seed(333)
a <- rnorm(20, 10, 1)
b <- rnorm(20, 15, 2)
c <- rnorm(20, 20, 3)
grp <- rep(c('m', 'y'),10)
test_data <- data.frame(a, b, c, grp)

Output result

#         mean in group m mean in group y   p.value
# a ~ grp        9.775477        10.03419 0.5654353
# b ~ grp       14.972888        14.81895 0.8678149
# c ~ grp       20.383679        20.74238 0.7776188